Optical discs, such as DVDs, are commonly used for storing data and viewing video content. Optical discs provide the ability to reproduce moving pictures and sound, and provide durability and interactivity. Optical discs are commonly provided with one or more layers to which data may be recorded. Data may be recorded on a spiral track on the optical disc. The data may comprise a lead-in area, a data area, and a lead-out area. The data area may include a volume descriptor which identifies the structure and contents of the data area, together with one or more tracks.
The DVD specification was adopted by movie and home entertainment distributors as a technology for distributing movies to customers in the home entertainment marketplace. Pre-recorded DVDs are mass-produced using molding machines that physically stamp data onto the DVD. Such discs are known as DVD-ROMs (DVD-Read Only Memory), because data may be read but not written or erased. Blank recordable DVD discs (DVD-R and DVD+R) may be recorded once using a DVD recorder and then function as a DVD-ROM. DVD-Download discs provide CSS (Content Scramble System) managed recordings with a similar capacity as DVD-ROM or DVD-R discs. DVD-Download discs may be used for manufacturing DVDs on demand using similar copy protection schemes as are used on commercial DVDs.